a) Field of the Invention
This invention relates to a device and a method for filtering a liquid to remove impurities therefrom. More particularly, the present invention is involved with solving the problem resulting from the evacuation of various polluting agents in the environment and is especially concerned with the treatment of industrial waste water, leaching water from sanitary refuse, drained water from mining residues, septic tank sludge, and water resulting from the melting of snow.
b) Description of Prior Art
The polluting agents which are mostly found in the above-mentioned effluents include materials in suspension, metals, oils and greases, organic compounds and the like. The pH of these effluents varies from acid to slightly basic.
The filtration processes which are presently available generally use only one filtrating medium may rely on peat, activated carbon, sand or gravel.
The purifying property of peat has been known for a long time. The prior art (Meunier, F. 1985, Utilisation de la tourbe pour le traitement des eux usees. John Meunier Inc., Dept. Recherche et Dev., Montreeal; Nichols and Boelter, Treatment of Secondary Sewage Effluent with a Peat-Sand Filter Bed, J. Environ. Qual., Vol. 11, no. 1, 1982; Rock et al., Use of Peat For On-Site Wastewater Treatment: I. Laboratory evaluations. J. Environ. qual. 13: 518-523, 1984; Brooks et al. Use of Peat for On-Site Wastewater Treatment: II. Field Studies, J. Environ. Qual., Vol. 13, no. 4, 1984) describes applications for the treatment of waste water, effluents from septic tanks or leaching water, where filtration with peat enables to remove solids, metals and organic materials.
Filtering with activated carbon makes use of adsorption phenomenons because of its very high specific surface (1000 to 1500 m.sup.2 /g). Activation of carbon produces a porous structure with an increased specific surface. However, the production of activated carbon is costly because it is high energy consuming with the result that filtration of highly contaminated water with activated carbon is only carried out under exceptional circumstances.
On the other hand filtration with a bed of sand is mostly used in plants for the production of drinking water.
To applicant's knowledge, there is no teaching in the prior art of an effective treatment to remove substantially all the above undesirable polluting agents from waste water.
The following references are however of interest:
UNITED STATES PATENTS:
5,013 PA2 89,353 PA2 521,650 PA2 560,261 PA2 600,451 PA2 847,518 PA2 869,188 PA2 956,832 PA2 2,328,381 PA2 15,132 PA2 154,782 PA2 751,378 PA2 1,110,559 PA2 1,164,416 PA2 521,903 PA2 50-47447 PA2 51-65113 PA2 244310 PA2 1,815,136 PA2 161,912
BRITISH PATENTS:
U.S.S.R. PATENT:
JAPANESE PATENTS
GERMAN PATENT
EUROPEAN PATENT
It is therefore an object of the present invention to provide a solution to the evacuation of various polluting agents in the environment.
Is is another object of the present invention to provide a device and a method of filtering a liquid to remove impurities therefrom which is highly efficient, is simple to operate and is not too costly.
It is another object of the present invention to provide a device and a method of filtering which is based on a new combination of filtrating media whereby the efficiency results from the synergism of certain filtrating media, which are used separately in conventional filtration processes.
It is another object of the present invention to provide filtration media incorporating a new medium which achieves more satisfactory results and enables to reach a higher degree of purification, while greatly increasing the treatment yield.